When mooring a container ship or similar large vessel to a dock, in order to inhibit damage to the ship or the dock, a mooring robot is generally provided that is adequately strong to resist the forces exerted on it by the action of the wind, waves, passing vessels and tide. The mooring robot also accommodates relative vertical movement between the dock and the ship due to variations in tides and displacement. Further, the mooring robot should permit the connection between the ship and the dock to be made or broken quickly without damage to either the dock or the ship. In view of the large size of the vessel typically used, the elements of a mooring robot must be structurally efficient in order to avoid the necessity of providing a large and heavy structure to withstand the significant forces which are encountered. It should also desirably have a low energy consumption.
Another desirable characteristic of a mooring robot, as discussed in WO 0162585, is the ability to absorb loads in the horizontal plane (i.e. external loads applied in the fore and aft direction and/or athwartships) to avoid the effects of impacts which could cause a loss of engagement. The ability to accurately control the position of a moored vessel is also an important requirement.
A disadvantage of the mooring robot and mooring system described in WO 0162585, however, is that fore and aft movement and vertical movement of the vessel relative to the mooring robot are accompanied by a component of movement athwartship, due to the telescoping arm of the robot being pivotably fixed. This feature makes accurately determining the position of the attachment elements complicated, and adds to the complexity of controlling the mooring robot. Also, since the plane of the vacuum cups is not maintained parallel to the surface of the hull with which it engages, additional wear of the vacuum seals may result as the cups are often pivoted as they first engage the hull. A further disadvantage of this, and like devices, is that the telescopic booms, being subject to significant bending loads, must be relatively massive and that, even with the arms retracted, the device requires significant space at the front mooring face of the dock.
WO 9114615 describes a mooring device that attempts to overcome some of the problems associated with the large bending moments exerted by longitudinal movement of the ship, parallel to the face of the dock. One of the solutions proposed is the incorporation of a spherical joint into a fastening mounted on the ship. Such a design however, requires the mooring device to be specially adapted, as well as a large degree of precision to align the two mechanical coupling components. Another solution is to take the longitudinal loads through stay lines, however the stays obstruct a significant area of the face of the dock.
All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.